The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include internal combustion engines that generate drive torque. Intake valves are selectively opened to draw air into cylinders of the engine. The air is mixed with fuel to form a combustion mixture. The combustion mixture is compressed and combusted within the cylinders to drive pistons therein. Exhaust valves are selectively opened to allow the exhaust gas to exit from the cylinders after combustion.
Timing for opening and closing the intake and exhaust valves may be controlled by an intake camshaft and an exhaust camshaft, respectively. The camshafts are synchronized with a crankshaft by a chain or belt and generally include cam lobes that correspond to the plurality of intake and exhaust valves.
Valve lifters are provided between the intake and exhaust valves and the intake and exhaust camshafts for controlling opening and closing of the intake and exhaust valves. The valve lifters for the intake valves may be two-step valve lifters that are selectively operable in a low-lift state and a high-lift state. When engine load is low, the valve lifters are switched to a low-lift state to reduce displacement of the intake valves to reduce engine pumping losses. When engine load is high, the valve lifters are switched to the high-lift state to allow for a greater displacement of the intake valves, resulting in a greater open duration for the intake valves. Additionally, the valve lifters that have different lift profiles may change the duration and timing of the valve event to allow for early intake valve closing (EIVC) or late intake valve closing (LIVC).